The evolution of cellular communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. As a result, during the course of a single call, a wireless mobile station may roam among multiple radio access networks (RANs), wherein each such RAN implements a different technology than the other RANs of the multiple RANs. Some examples of the different packet data network technologies include cdma2000 high rate packet data (HRPD) also known as 1xEV-DO (1X Evolution Data Only), cdma2000 1XRTT, cdma2000 1x-EV-DV (1x Evolution Data/Voice), IEEE 802.11b/g, and IEEE 802.16. An example of a circuit RAN is a cdma2000 1X RAN providing only circuit voice or circuit data service.
As the mobile station roams among a circuit services RAN, such as a cdma2000 1X RAN, and a packet data RAN providing packet data services, it may be beneficial to system performance to handoff the mobile station from the circuit services RAN to the packet data RAN. For example, the channel conditions associated the latter RAN may be more favorable than the channel conditions associated with the former RAN due to such factors as fading, adjacent and co-channel interference, and available power at a serving base station (BS) or radio access network (RAN). By way of another example, an operator of both a legacy circuit network and an HRPD network may desire to move the mobile station from one such network to the other network for purposes of system loading.
Currently, the only defined method for executing a handoff from a legacy cdma2000 1X circuit services RAN to an HRPD packet data RAN is an execution of a dormant hard handoff as defined by the 3GPP2 (Third Generation Partnership Project 2) A.S0008-B v0.2 and A.S0009-B v0.2 HRPD Inter Operability Specification (IOS) standards (V&V versions), wherein a mobile station must go dormant and drop a radio resource of a network of a first cdma2000 technology and then acquire a radio resource of a network of a second cdma2000 technology. A result is a brief period of time during which the mobile station is not actively engaged in a communication session with either network. Further, when executing a dormant hard handoff there is no linkage between the two networks as the mobile station must drop the first network and acquire the second network without any assistance from the BS or AN of either network. As a result, voice/data traffic may be lost during the handoff, resulting in poor system performance and efficiency and disgruntled end users.
Therefore, a need exists for a method and apparatus for implementing an active hard handoff of a communication session from a circuit services RAN providing circuit voice and data services support to a packet data RAN providing packet data services support that minimizes an amount of time that a mobile station is not actively engaged in a communication session with either network during the handoff.